The Environmental Protection Agency (EPA) requires vehicle manufacturers to install on-board diagnostics (e.g., microcontrollers and sensors, called ‘OBD-II systems’) for monitoring light-duty automobiles and trucks beginning with model year 1996. OBD-II systems monitor the vehicle's electrical, mechanical, and emissions systems and generate data that are processed by a vehicle's engine control unit (ECU) to detect malfunctions or deterioration in the vehicle's performance. Most ECUs transmit status and diagnostic information over a shared, standardized electronic buss in the vehicle. The buss effectively functions as an on-board computer network with many processors, each of which transmits and receives data.
Sensors that monitor the vehicle's engine functions (e.g., spark controller, fuel controller) and power train (e.g., engine, transmission systems) generate data that pass across the buss. Such data are typically stored in random-access memory in the ECU and include parameters such as vehicle speed (VSS), engine speed (RPM), engine load (LOAD), and mass air flow (MAF). Some vehicles (e.g., certain 2001 Toyota Camrys) lack a MAF sensor, in which case the MAF datum is not available from the ECU. Nearly all OBD-compliant vehicles, however, report VSS, RPM, and LOAD. When present, these and other data are made available through a standardized, serial 16-cavity connector referred to herein as an ‘OBD-II connector’. The OBD-II connector is in electrical communication with the ECU and typically lies underneath the vehicle's dashboard. A diagnostic tool called a ‘scan tool’ typically connects to the OBD-II connector and downloads diagnostic data when a vehicle is brought in for service.